Electrospraying apparatus and method for coating particles

ABSTRACT

An electrospraying apparatus and/or method is used to coat particles. For example, a flow including at least one liquid suspension may be provided through at least one opening at a spray dispenser end. The flow includes at least particles and a coating material. A spray of microdroplets suspending at least the particles is established forward of the spray dispenser end by creating a nonuniform electrical field between the spray dispenser end and an electrode electrically isolated therefrom. The particles are coated with at least a portion of the coating material as the microdroplet evaporates. For example, the suspension may include biological material particles.

The present application is a divisional application of Ser. No.10/162,031, filed on Jun. 3, 2002 now U.S. Pat. No. 6,746,869, entitledELECTROSPRAYING APPARATUS AND METHOD FOR COATING PARTICLES, which is acontinuation application of Ser. No. 09/577,747 filed on May 23, 2000,issued as U.S. Pat. No. 6,399,362, which is a divisional application ofSer. No. 09/092,794 filed on Jun. 5, 1998, issued as U.S. Pat. No.6,093,557, which claims benefit of 60/049,444 filed on Jun. 12, 1997,all of which are incorporated by reference herein.

BACKGROUND OF THE INVENTION

Various devices and methods for use in genetic transformation of plantand animal cells have been utilized and many others have been describedin various publications. For example, a few early techniques foraccomplishing the transport of substances, e.g., DNA, into cells,include uptake mechanisms, fusion mechanisms, and microinjectionmechanisms. Generally, uptake mechanisms include the use of substances,such as, for example, liposomes, which encapsulate substances andfacilitate transfer of the substances to the cell through fusion of theliposomes with the cell membrane, electroporation, calcium chlorideprecipitation, and the like. These uptake protocols generally are quitesimple and allow for treatment of large numbers of cells at one time,but this technique tends to have a very low efficiency, i.e.,transformation frequency is low.

Generally, fusion mechanisms incorporate genetic material into a cell byallowing a cell to fuse with a membrane compatible with the cellmembrane of the cell. The fusion of two cells can be used forintroducing material into a cell. Cell fusion technologies may havebetter efficiencies than uptake mechanisms, but cell selection can bemore complex, and the resulting cells are typically of elevated ploidy,which makes them of limited use.

Microinjection mechanisms typically employ extremely fine, drawn outcapillary tubes, which are sometimes micropipettes or needles. Thesecapillary tubes can be made sufficiently small to be used as syringeneedles for the direct injection of biological material into certaintypes of individual cells. When very small cells are to be injected,very sharp capillary tubes are required, whose tips are very easilybroken or clogged. High pressures are required to cause bulk flowthrough the small orifices and regulation of such flow is difficult. Aform of microinjection, commonly referred to as ionophoresis, is alsoused. Ionophoresis utilizes electrophoresis of substances out of amicroelectrode and into a cell, as an alternative to high pressure bulkflow. Although efficiency of microinjection, as one might expect ishigh, transformation of individual cells is by single cell manipulationand therefore treatment of masses of cells is difficult.

More recently, various techniques involving acceleration of substancesfor bombardment with cells to accomplish gene transfer have been usedand described, e.g., gene guns. For example, such techniques include theuse of mechanical impact to project such substances, the use ofelectrostatic acceleration of the substances, and/or the use ofelectrostatic discharge to project such substances. It has been statedthat such techniques allow the substances to attain a velocity enablingthem to penetrate cells.

Various forms of accelerating the substances, for example, are describedin the gene gun patent to Sanford et al., U.S. Pat. No. 4,945,050entitled “Method for Transforming Substances into Living Cells andTissues and Apparatus Therefor.” As described therein, for example, amechanical shock is applied to a layer of particles (e.g., gold), whichare coated, impregnated, or otherwise associated with biologicalmaterial. The impact causes the particles to be accelerated such thatthe particles hit the cells to be transformed downstream of theapparatus causing the mechanical shock. The particles puncture the cellmembrane and enter the cell, releasing the biological material into thecells.

Spark discharge techniques for accelerating the particles, as describedin U.S. Pat. No. 5,120,657 to McCabe et. al., includes the use of aspark discharge chamber. The chamber includes electrodes spaced by aspark gap. A movable particle carrier is moved when a spark discharge inthe chamber creates a shock wave that accelerates the movable particlecarrier such that the movable particle carrier hits another objectaccelerating the cells for impact with the target cells to betransformed.

However, such mechanical shock techniques have various disadvantages.First, the techniques are generally batch techniques, i.e., theytransfer a certain batch of coated or impregnated particles. If moreparticles than the number of particles in a single batch are to betransferred, another run or batch must be initiated. For example, thismay involve reloading or replacing a part of the apparatus containingthe particles, e.g., the movable particle carrier described above.

Further, the coated or impregnated particles when positioned on thetransfer surface, e.g., such as the movable particle carrier, may beagglomerated, or such agglomeration may occur during the transfer.Agglomeration of the particles may cause undesirable pit damages to thetarget cells upon impact therewith.

Yet further, preparation of coated or impregnated particles is a timeconsuming process. For example, it may take one or more days toprecipitate coated or impregnated particles out of a solution containingthe carrier particles and the biological material to be transferred.

In addition, the overall process is not easily controlled. For example,there is typically only a limited range of impact velocity which thecoated or impregnated particles may attain. The type and origin of thecell can influence the velocity necessary for transformation. Thus,devices that can produce a broader range of impact velocities aredesirable. Further, for example, the delivery of particles uniformly tothe target cells is not easily controlled. As such, target cells locatedat certain positions may be damaged more easily than those target cellssurrounding such positions. For example, target cells located at thecenter of a batch of target cells may be damaged or killed more readilythan those in the surrounding target-area when bombarded by coated orimpregnated particles by conventional batch gene gun devices. This maybe at least in part due to the agglomeration of the particles. As theoverall process is not easily controlled, the amount of biologicalmaterial being delivered to the target cells is not readilycontrollable.

Other acceleration techniques, such as aerosol beam technology,electrostatic acceleration fields, centrifugal techniques, etc. asdescribed in U.S. Pat. No. 4,945,050; International Publication WO91/00915 entitled “Aerosol Beam Microinjector;” and various and numerousother references, may not include all of the disadvantages as describedabove with regard to the use of mechanical shock. However, suchtechniques do not alleviate all of such problems. For example, theaerosol technique may allow for a more continuous transfer method asopposed to a batch method, but still has the associated agglomerationdisadvantages.

For the above reasons, there is a need in the art for gene transfermethods and apparatus which reduce the effect of such disadvantages asdescribed above. The present invention overcomes the problems describedabove, and other problems as will become apparent to one skilled in theart from the detailed description below.

SUMMARY OF THE INVENTION

A method of introducing biological material into cells according to thepresent invention includes providing one or more target cells andestablishing a spray of substantially dispersed particles includingbiological material. The substantially dispersed particles have anelectrical charge applied thereto such that one or more of thesubstantially dispersed particles of the spray is introduced into one ormore of the target cells.

In one embodiment of the method, the step of establishing the spray ofsubstantially dispersed particles includes dispensing a spray ofmicrodroplets suspending particles. The electrical charge isconcentrated on the suspended particles as the microdroplets evaporate.

In various embodiments, the suspended particles may include carrierparticles having biological material associated with the carrierparticles or the suspended particles may be particles of biologicalmaterial. The spray may also be a charged spray of powdered biologicalmaterial.

Further, in yet another embodiment, the step of dispensing the spray ofmicrodroplets suspending particles may include creating a nonuniformelectrical field between a dispensing tip from which the spray isestablished and an electrode electrically isolated from the dispensingtip. The substantially dispersed particles may be directed towards theone or more target cells using the electrode isolated from thedispensing tip.

In another embodiment, the space charge effect of the concentratedelectrical charge on the substantially dispersed particles of the sprayenable one or more of the particles to be introduced into one or more ofthe target cells. The electrical charge concentrated on a particularparticle is in the range of about 80 percent to about 95 percent of amaximum charge that can be held by the microdroplet suspending theparticular particle.

Yet further, in another embodiment of the method, the step ofestablishing a spray of substantially dispersed particles includesestablishing a continuous spray of substantially dispersed particles.

An apparatus for introducing biological material into one or more targetcells according to the present invention includes a biological materialsource including at least biological material. The apparatus furtherincludes a dispensing device operably connected to the biologicalmaterial source to receive at least biological material from thebiological material source. The dispensing device provides a spray ofsubstantially dispersed particles of at least the biological material.Further, the spray of substantially dispersed particles has anelectrical charge applied thereto such that one or more of thesubstantially dispersed particles of the spray is introduced into one ormore of the target cells.

In one embodiment of the apparatus, the biological material sourceincludes a suspension source. The suspension source includes asuspension of at least biological material. Further, the dispensingdevice receives the suspension and dispenses a spray of microdropletssuspending particles of at least biological material.

In another embodiment, the dispensing device includes a dispensing tipfrom which the spray of microdroplets suspending particles is dispensedand an electrode isolated from the dispensing tip. A nonuniformelectrical field is created between the dispensing tip and theelectrode. Generally, the electrode, e.g., a ring electrode or aconductive target surface, is located at a position relative to thedispensing tip to direct the spray of substantially dispersed particlestowards the one or more target cells. The target and the dispensingdevice may be movable relative to each other, e.g., a distance betweenthe dispensing device and the target may be adjusted.

Another apparatus for introducing biological material into target cellsaccording to the present invention includes a biological material sourceincluding a suspension of at least biological material. The apparatusfurther includes a capillary tube electrode. The capillary tubeelectrode includes a capillary tube having a first open end and a secondopen end with the capillary tube operatively connected to the biologicalmaterial source to receive a flow of the suspension of at leastbiological material at the first open end thereof. The apparatus furtherincludes an electrode isolated from but positioned in proximity to thesecond open end of the capillary tube. A nonuniform electrical field iscreated between the capillary tube electrode and the electrode such thata spray of microdroplets suspending particles of at least biologicalmaterial is provided from the second end of the capillary tube. Further,upon evaporation of the microdroplets an electrical charge isconcentrated on the suspended particles resulting in a charged spray ofsubstantially dispersed particles such that one or more of thesubstantially dispersed particles of the spray is introduced into one ormore of the target cells.

In one embodiment of the apparatus, the capillary tube electrode furtherincludes a casing concentric with at least a portion of the capillarytube between the first and second open ends thereof. The second open endof the capillary tube extends beyond the casing a predetermineddistance. The apparatus further includes a gas source providing a gas tobe received between the capillary tube and the concentric casing.

Yet another apparatus for introducing biological material into targetcells according to the present invention is described. The apparatusincludes a biological material source including a suspension of at leastbiological material and an electrolyte source for providing a solution.The apparatus further includes a capillary tube electrode having adispensing tip. The capillary tube electrode includes a first capillarytube having a first open end and a second open end with the firstcapillary tube operatively connected to the biological material sourceto receive a flow of the suspension of at least biological material atthe first open end thereof. The capillary tube electrode furtherincludes a second capillary tube concentric with at least a portion ofthe first capillary tube. The solution is received in an annular openingdefined between the first and second concentric capillary tubes. Yetfurther, the apparatus includes an electrode isolated from butpositioned in proximity to the dispensing tip of the capillary tubeelectrode. A nonuniform electrical field is created between thecapillary tube electrode and the electrode such that a spray ofmicrodroplets suspending particles of at least biological material isprovided from the dispensing tip. Upon evaporation of the microdroplets,an electrical charge is concentrated on the suspended particlesresulting in a charged spray of substantially dispersed particles.

Another method for introducing biological material into target cellsaccording to the present invention includes providing one or more targetcells, providing a first flow of a suspension including at leastbiological material, and providing a second flow of electrolytesolution. A spray of substantially dispersed particles including atleast biological material is established from the first flow and thesecond flow. The substantially dispersed particles have an electricalcharge applied thereto such that one or more of the substantiallydispersed particles of the spray is introduced into one or more of thetarget cells.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a general block diagram representative of an electrosprayingapparatus in accordance with the present invention for establishing acharged spray using a biological material source.

FIG. 1B is a general diagrammatical illustration of an electrosprayingapparatus in accordance with the present invention for establishing acharged spray using a biological material source including a suspension.

FIG. 1C is one embodiment of the electrospraying apparatus of FIG. 1B inaccordance with the present invention for establishing a charged sprayusing a capillary tube electrode and a biological material sourceincluding a suspension.

FIG. 2 is a diagrammatical illustration of another embodiment of anelectrospraying apparatus of FIG. 1B in accordance with the presentinvention.

FIG. 3 is a diagrammatical illustration of the apparatus shown in FIG. 2including an additional electrostatic acceleration field.

FIG. 4 is a diagrammatical illustration of the apparatus of FIG. 2including a placement control member.

FIG. 5 is a diagrammatical illustration of an alternate electrosprayingapparatus in accordance with the present invention using a vacuumchamber.

FIG. 6 is a further alternate electrospraying apparatus in accordancewith the present invention illustrating a continuous electrosprayingapparatus.

FIG. 7 is a more detailed diagram of a portion of the electrosprayingapparatus in accordance with the present invention having a singlecapillary tube distributor head.

FIG. 8 is a more detailed diagram of an alternate capillaryconfiguration for use in the apparatus shown in FIG. 7 including a dualcapillary tube distributor head.

FIG. 9 shows an illustrative diagram of a portion of a compact pen-likeelectrospraying apparatus in accordance with the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention shall first generally be described with referenceto FIGS. 1A-1C. Various other embodiments of the present invention shallthen be described further with reference to FIGS. 2-9. It will becomeapparent to one skilled in the art that elements from one embodiment maybe used in combination with elements of the other embodiments and thatthe present invention is not limited to the specific embodimentsdescribed herein but only as described in the accompanying claims.

The present invention is directed to apparatus and methods forintroduction of biological materials, such as, for example, DNA, intotarget cells, e.g., plant or animal cells. As shown in FIG. 1A, thepresent invention uses an electrospraying apparatus 1 to establish aspray 4 of charged particles. The electrospraying apparatus 1 includes adispensing device 3 which receives at least biological material from abiological material source 2 and establishes the charged spray 4 forwardthereof. The space charge effect of the charged particles of the spray 4enable the particles to attain a velocity such that the particlesforcibly contact, and preferably, penetrate target cells 5 whenimpacted.

As used herein the term charged spray 4 shall refer to a spray ofparticles having a charge applied thereto established from a source ofbiological material 2. The source of biological material may be a sourceof dry biological material alone or biological material associated withcarrier particles, i.e., a powdered form of biological material.Preferably, the source of biological material 2 is a suspension ofbiological material, i.e., a solution including at least biologicalmaterial. For example, the suspension of biological material may be asuspension of biological material alone or a suspension of biologicalmaterial and carrier particles. However, any source of biologicalmaterial which can be sprayed with a unipolar charge (i.e., a samepolarity charge) applied thereto can be used according to the presentinvention.

The dispensing device 3 may be any device for establishing a spray ofcharge particles 4 with a unipolar charge applied thereto such that thespace charge effect of the charged particles of the spray 4 enable theparticles to attain a velocity allowing the particles to forciblycontact, and preferably, penetrate the target cells 5. The configurationof the dispensing device 3 will depend at least upon the type ofbiological material source 2 used. For example, when the biologicalmaterial source 2 is a source of dry biological material alone orbiological material associated with carrier particles, i.e., a powderedform of biological material, the dispensing device 3 may take the formof a spraying device which applies a unipolar charge to the particles ofthe spray using corona discharge. Such a spraying device may include astructure having an orifice therethrough. A flow of the powderedmaterial may be provided through the orifice, e.g., by way of apressurized gas source. Upon exit from the orifice, the particles of thespray may be subjected to a weak corona established by brushespositioned about the orifice. One skilled in the art will recognize thatthis is just one illustrative example of a device for spraying powderedbiological material with a charge applied thereto and that the presentinvention is clearly not limited to this particular embodiment but islimited only as described in the accompanying claims.

As one skilled in the art will recognize, as used herein, the termapplied charge refers to applying a unipolar charge (e.g., the samepolarity charge) to the particles of spray 4. For example, the chargemay be applied by corona discharge as described above with reference topowdered biological material. Further, for example, the charge may beapplied by concentration of charge on the spray of particles throughevaporation of solution suspending the particles in an establishedelectrical field as further described below with respect to the generalillustration of FIG. 1B. In other words, for example, the biologicalmaterial source 2 is a suspension of biological material and a spray ofmicrodroplets is dispensed from the dispensing device 3, i.e., particlessuspended by microdroplets are dispensed. The particles suspended bymicrodroplets may be carrier particles and biological material orbiological material itself without the use of carrier particles. Inother words, when dispensed, the spray is preferably a spray of liquidsuspended particles as opposed to a powder spray. The liquid portion ofthe spray of suspended particles generally evaporates to concentrate thecharge of the liquid portion on the particles resulting in a spray ofcharged particles as will be described further below with reference toFIG. 1B.

The spray of particles provided by electrospraying provides for acontrollable biological material transfer process which is not limitedto batch processing. Rather, the electrospray technique may be utilizedin a continuous manner.

The electrospraying mechanism 1 provides a charged spray with a highconcentration of charged particles. Preferably, the concentration ofcharged particles in the spray is in the range of about 10⁵particles/cubic centimeter (particles/cc) to about 10¹² particles/cc;more preferably in range of about 10⁷ particles/cc to about 10¹⁰particles/cc; and further even more preferably about 10⁹ particles/cc.Below about 10⁵ particles/cc, the concentration of charged particles isto low for the space charge effect to attain a velocity for introductioninto most target cells. Due to the space charge effect, i.e., the effectcreated by the charge repulsion of charged particles, a spray ofsubstantially dispersed particles having the same polarity charge isprovided with the particles distributed substantially uniformly acrossthe spray area (e.g., the area represented by D in FIG. 1A) wherein thetarget cells are placed. As used herein, the term substantiallydispersed particles refers to uniformly and/or nonuniformly sizedparticles separated by an applied repulsive electrostatic force. Thus,the electrospray process is a consistent and reproducible transferprocess. Further, because the charged particles of the spray repel fromone another, agglomeration of the particles is avoided. As such, theelectrospray technology provides for reduced cell pit damage and shockinjury which are common results when particle agglomeration occursutilizing conventional methods of transfer. In addition, as describedbelow, the electrospraying technique allows the gene transfer process tobe controlled in various manners.

Due to the small size of the charged particles of the spray establishedin the region of a target including one or more cells, the space chargeeffect, i.e., the effect created by the charge repulsion of chargedparticles, provides particles having sufficient velocity to forciblycontact, and preferably penetrate, one or more target cells. However,such space charge effect also creates a spray of charged particles thatis generally not contained, i.e., the particles randomly disperse inmultiple directions. Therefore, it is preferable to confine or directthe spray of charged particles towards the one or more target cells. Asillustrated below, one technique of providing such containment and/ordirection for such charged particles is to use an electrode alreadyrequired to establish the charged spray when the biological materialsource is a suspension of at least biological material. In other words,the electrode is used to provide a nonuniform electric field forestablishing a charged spray and also provides direction for theparticles of the charged spray as is described further below.

FIG. 1B generally shows a diagrammatical illustration of anelectrospraying apparatus 6 for establishing a charged spray 28 using adispensing device 8 which receives a flow of a suspension from abiological material source 7. The biological material source 7 containsa suspension of at least biological material, e.g., biological materialalone or biological material and carrier particles. Generally, thedispensing device 8 includes a conductive structure 17 defining anorifice 9 (e.g., a capillary tube, an orifice defined in a floodingchamber, etc.) for receiving a flow of solution suspending particles,e.g., biological material alone or carrier particles along withbiological material. For example, the solution may be pushed or pulledthrough the orifice 9 at dispensing tip 27 of the conductive structure17 defining the orifice 9, e.g., pushed by a pump. The conductivestructure 17 defining the orifice 9 functions as a first electrode ofthe dispensing device 8 with the dispensing tip 27 of the conductivestructure positioned for dispensing microdroplets towards target cells5. Further the dispensing device 8 includes a second electrode structure11. An electrical potential difference is applied between the firstelectrode 17 and second electrode 11 to create a nonuniform electricfield between the first electrode 17 and second electrode 11. Oneskilled in the art will recognize that the electrodes may be formedusing one or more conductive elements.

Generally, in operation, a flow of the suspension is provided throughthe orifice 9, e.g., pushed and/or pulled through the orifice 9. Ameniscus is formed at the dispensing tip 27 where the orifice 9 has adiameter in the preferred range of about 6 microns to about 2millimeters (mm). A potential difference is applied to establish anonuniform field 15 between the first electrode 17 and second electrode11. For example, a high positive voltage may be applied to the firstelectrode 17 with the second electrode 11 being grounded. Further, forexample, a voltage difference in the preferred range of about 2000 voltsto about 6000 volts may be applied.

As used herein, nonuniform electric field refers to an electric fieldcreated by an electrical potential difference between two electrodes.The nonuniform electric field includes at least some electric fieldlines that are more locally concentrated at one electrode relative tothe other electrode, e.g., more concentrated at the dispensing tiprelative to the second electrode. In other words, for example, at leastsome of the field lines are off-axis relative to a longitudinal axis 29through the center of the orifice 9. Further, for example, the electrode11 is positioned forward of the dispensing tip 27 towards the targetcells 5 and the electrode 11 is of a size and/or includes at least aportion that is located at a position away from the longitudinal axis29. Yet further, for example, the electrode 11 may be a ring electrodehaving a diameter larger than the diameter of the orifice 9 andpositioned forward of the dispensing tip 27 with an axis through thecenter of the ring electrode coincident with the longitudinal axis 29 ofthe orifice 9. Further, for example, the electrode 11 may be aconductive target surface having an area greater than a cross sectionarea taken through the orifice 9 perpendicular to the longitudinal axis29 and positioned forward of the dispensing tip 27.

In the case where the biological material source 7 is a suspension ofbiological material (without the use of carrier particles), thesuspension is flowed (e.g., pushed and/or pulled) through the orifice 9.Generally, the liquid portion of the suspension provided to the orifice9 has an electrical conductivity. The biological material generally hasa small charge associated therewith, e.g., DNA may have a small negativecharge, but the charge of the biological material is inconsequential dueto the larger charge concentrated on the biological material asdescribed below.

As the suspension progresses through the orifice, the potentialdifference between the first and second electrodes which creates theelectrical field therebetween strips the liquid of one polarity ofcharge, i.e., the negative charge is stripped when a high positivevoltage is applied to the electrode 17, leaving a positively chargedmicrodroplet to be dispensed from the dispensing tip 27. For example,the meniscus at the dispensing tip may form a cone jet for dispensing aspray of microdroplets suspending biological material when the forces ofthe nonuniform field 15 balances the surface tension of the meniscus.The spray of microdroplets further become more positive in thenonuniform electric field 15.

As the microdroplets evaporate, the charge of the microdropletsconcentrate on the biological material resulting in a spray of chargedbiological material particles. The amount of charge on the microdroplet,and thus the amount of charge on a particle after evaporation, is basedat least upon the conductivity of the liquid used to spray themicrodroplets, the surface tension of the liquid, the dielectricconstant of the liquid, and the feed flow rate of the liquid. Generally,the space charge effect due to the concentrated electrical charge on thesubstantially dispersed particles of the spray enable the particles toforcibly contact, and preferably, penetrate the target cells. Theelectrical charge concentrated on a particular particle is preferably inthe range of about 80 percent to about 95 percent of a maximum chargethat can be held by the microdroplet suspending the particular particle,e.g., biological material particle, without the microdroplet beingshattered or torn apart, i.e., in the range of about 80 percent to about95 percent of the Rayleigh charge limit. At 100 percent, the surfacetension of the microdroplet is overcome by the electrical forces causingdroplet disintegration. The nonuniform electrical field also providesfor containment of the particles and/or direction for the particleswhich would otherwise proceed in random directions due to the spacecharge effect.

In the case where the biological material source 7 is a suspension ofbiological material and carrier particles, the suspension is flowed(e.g., pushed or pulled) through the orifice 9. Generally, the liquidportion of the suspension provided to the orifice 9 has an electricalconductivity. As will be described below, more than one flow of solutionmay be used to establish the spray. For example, one flow of materialmay be a suspension of material using deionized water with a second flowof material including an electrolyte solution having a suitableconductivity. The biological material generally has a small butinconsequential charge associated therewith. The carrier particles aregenerally neutral.

As the suspension progresses through the orifice, the potentialdifference between the first and second electrodes which creates thenonuniform electrical field therebetween strips the liquid of onepolarity of charge, i.e., the negative charge is stripped when a highpositive voltage is applied to the electrode 17, leaving a positivelycharged microdroplet to be dispensed from the dispensing tip 27. A sprayof microdroplets suspending biological material and carrier particles isestablished forward of the dispensing tip 27 with the microdropletsbeing positively charged.

As the microdroplets evaporate, the charge of the microdropletsconcentrate on the biological material and carrier particles resultingin a spray of positively charged carrier particles associated withbiological material. The biological material, which may carry a slightlynegative charge, are attracted to the positively charged carrierparticles resulting in better adhesion between the biological materialand the carrier particles. This is unlike conventionally preparedcarrier particles having associated biological material because inconventional processes the neutral carrier particles do not create suchattraction forces with the slightly negatively charged biologicalmaterial. In other words, the present invention provides a bettercoating process for coating carrier particles with biological material.This results in more uniform distribution of biological material beingdelivered to the target cells. Generally, as described above, the spacecharge effect due to the concentrated electrical charge on thesubstantially dispersed particles of the spray enable the particles toforcible contact, and preferably, penetrate the target cells.

One skilled in the art will recognize that the voltages applied may bereversed. For example, the first electrode may be grounded with a highpositive voltage applied to the second electrode. In such a case, theparticles of the spray would have a negative charge concentratedthereon. Further, any other applied voltage configuration providing anonuniform electrical field to establish the charged spray of particlesmay be used.

Further, one skilled in the art will recognize that the spray ofparticles need not have the biological material associated with thecarrier particles. For example, if a positive voltage is applied to thesecond electrode 11 and the first electrode 17 is grounded, then thecarrier particles which are normally neutral in the suspension will havea negative charge thereon as they are spray. With biological materialbeing slightly negative, repulsion forces may keep the carrier particlesseparated from the biological material and therefore unassociatedtherefrom. In such a manner, for example, the carrier particles and thebiological material particles would be separate from one another in thespray of charged particles. The carrier particles may penetrate thetarget cells first forming a channel in the target cells such that thebiological material particles may easily travel therethrough forintroduction into the target cells.

One generalized embodiment of the electrospray apparatus 6 showngenerally in FIG. 1B shall be described with reference to theelectrospraying apparatus 10 shown in FIG. 1C. Generally, theelectrospraying apparatus 10 in accordance with the present inventionincludes an electrospray dispensing device 12 positioned for providing acharged spray 28. Downstream from or forward of the dispensing device 12is positioned a target 13 including one or more target cells 40.

In accordance with the present invention, the spray 28 has an electricalcharge applied thereto by way of a high positive voltage source 20applied to a capillary tube electrode 18 of distributor head 19 of theelectrospray dispensing device 12 and the electrode 21 being connectedto ground 38. The spray 28 is established as described above with use ofthe nonuniform electric field created between the dispensing tip 23 ofthe capillary tube electrode 18 and the electrode 21. The spray 28 maybe provided by any electrospray dispensing device suitable for providinga spray 28 having a charge applied thereto. Preferably, the charge ofthe particles is adequate for enabling the particles of the spray 28 tohave a velocity due to space charge effect sufficient for the dispersedparticles of the spray 28 to penetrate target cells 40.

The particle velocity is primarily a function of the particle charge andthe space charge effect. The nonuniform electric field formed betweenthe high voltage capillary tube electrode 18 and the electricallygrounded electrode 21 provides for the dispensing of the spray 28 fromthe dispensing tip 23 of distributor head 19. As described below,depending upon the potential difference applied between the distributorhead 19 having a first electrode, e.g., capillary tube electrode 18, andthe second electrode 21, different modes of spray operation can beestablished.

The nonuniform electric field can be provided by various configurations.For example, the second electrode 21 may be any conductive materialgrounded and positioned to establish the formation of a spray 28 fromthe dispensing tip 23 of the distributor head 19 or otherwise causingthe provision of a charged spray from the distributor head 19, e.g., thesecond electrode may be a grounded ring electrode, a grounded targetsurface holding the cells, etc. The second electrode 21 may be locatedat various positions as shown in FIG. 1C. For example, the electrode 21may be located at a position just forward of the distributor head 19, orthe electrode 21 may be located further away from the distributor head19 closer to the target cells 40.

It will be recognized that the second electrode 21 may take one of manydifferent configurations. For example, the electrode may be a conductiveplatform upon which the cells are positioned. Further, for example, theelectrode 21 may be a ring electrode having an axis coincident with anaxis of distributor head 19, etc. For the electric field to benonuniform, at least one portion of the electrode 21 must be positionedoutside of a hypothetical cylinder 25 extending from the perimeter ofthe capillary tube electrode to target 13. In other words, electricfield lines must extend to and/or from an area outside of thehypothetical cylinder 25.

The strength of the field may be adjusted by adjustment of the distancebetween the first electrode 18 and second electrode 21. The farther theelectrode 21 is from the distributor head 19, the lesser the fieldstrength. However, with such increasing distance, more directionality isprovided for the spray 28. For example, if the second electrode 21 isclose to the distributor head 19, the space charge effect will cause theparticles to disperse into a relatively large area D. On the other hand,the particles can be directed to various targets by moving the electrode21 to various positions. For example, the electrode 21, e.g., a ringelectrode, can be moved close to the target cells 40 to provide auniform spray 28 in the area proximate thereto.

The source 22 which provides biological material to feeder 24 may be oneof many types of biological material sources. Source 22 may be a liquidsuspension including biological material. Further, the liquid suspensionmay include a liquid suspension of bulk biological material (i.e.,without carrier particles), may be a liquid suspension of carrierparticles and biological material, or may be a liquid suspension ofcarrier particles having biological material associated therewith, e.g.,carrier particles coated or impregnated with DNA.

The present invention hereinafter shall primarily be described withreference to use of a source 22 that is a suspension of carrierparticles and biological material, e.g., DNA and gold particlesuspension. However, even though the description is focused to the useof a carrier particle suspension, the benefits of the present inventionare clearly applicable when other sources are used for providing chargedsprays as described herein. It will be recognized that carrier particlesof the suspension of carrier particles and biological matter need not becoated with the biological material prior to preparing and using thesuspension. In other words, generally, such a suspension is created bymixing the carrier particles and biological material into the suspensionliquid, e.g., buffer, electrolyte solution, deionized water, etc. Thisgenerally eliminates the substantially time consuming conventionalpreparatory processes involved in coating or impregnating carrierparticles for use in conventional batch gene gun devices.

The suspension may include any liquids suitable for biological materialdelivery. Further, a component of calcium chloride may be used in theliquid. Any solutions which are suitable for raising cells, such asnutriant solutions, may also be used. Further, for example, the liquidused in the suspension may be deionized water when an additionalconductive liquid is used therewith or when another flow of electrolytesolution is used with the flow of suspension to establish the spray ofparticles.

As known to one skilled in the art, various inert particles may be usedas the carrier particles. For example, such inert carrier particles mayinclude ferrite crystals, gold, tungsten spheres, and other metalspheres, as well as spheres and particles such as glass, polystyrene,and latex beads. Preferably, the carrier particles are only mixed in thesuspension with the biological material. However, such carrier particlesmay be coated or impregnated with biological material or otherwiseassociated therewith. For example, biological material may be coated on,bonded on, or precipitated onto the surface of the carrier particles orimpregnated with the biological material. As described above, thecarrier particles generally become associated with the biologicalmaterial as the suspension is spray. The carrier particles act as thecarrier for carrying the biological materials into the target cells.When one or more carrier particles having biological material associatedtherewith penetrate the cell membrane of the target cells, thebiological material is dispersed within the cell.

Biological material which can be used with the inert carrier particlesinclude but are not limited to biological stains such as fluorescent orradio-labeled probes, viruses, organelles, vesicles, peptides,ammoacids, lipids, proteins such as enzymes or hormones, nucleic acids,polynucleic acids including DNA and RNA, individual nucleic acids, smallmolecules such as bioactive substances, drugs, or the like. Thebiological material may be of a dry form or a wet solution. However, thepresent invention is clearly not limited to the materials listed herein.

Although it is preferred that a suspension of carrier particles andbiological material or a suspension of biological material be used inaccordance with the present invention, the present invention alsocontemplates other forms of biological material particles, i.e., in bothdry form or suspended. For example, such biological material particlesmay include biological material which is freeze-dried or otherwiseprepared as free particles or otherwise used as a particle for impactwith target cells to penetrate such cells. Once the biological materialparticles have penetrated the target cells, such biological materialparticles or portions thereof would be expected to return to theirnatural state undamaged or otherwise contribute a desired biologicalactivity within the target cell. For example, the biological materialparticles may return to their natural state by hydration, thawing,dissolving, etc.

The particle suspension from source 22 is provided to feeder 24 whichcontrols the continuous flow of the source material to the electrospraydispensing device 12 when operable. The feeder 24 may be a liquid pump(e.g., a syringe pump, a gravity feed pump, a pressure regulated liquidreservoir, etc.), a mass flow controller, or any other flow controldevice suitable for feeding the source material to the dispensing deviceas would be known to one skilled in the art. The flow of a particlesuspension, i.e., a solution, is atomized into microdroplets by thedispensing device 12. Atomization may be provided by any known techniquefor producing microdroplets, which microdroplets preferably have anominal diameter of about 10 nm or greater, more preferably about 20 nmto about 10 μm, and even more preferably about 30 nm to about 1 μm.Preferably, electrostatic atomization is used. However, otheratomization devices (e.g., pressure regulated atomizers, ultrasonicnebulizers, hydraulic nozzles, etc.) may provide adequate atomization.As described in the papers entitled, “Electrospraying of ConductingLiquids for Dispersed Aerosol Generation in the 4 nm to 1.8 μm DiameterRange, by Chen et al., J. Aerosol Sci., Vol. 26, No. 6, pp. 963-977(1995) and entitled “Experimental Investigation of Scaling Laws forElectrospraying: Dielectric Constant Effect,” by Chen et al., AerosolScience and Technoloy, 27:367-380 (1997) which are hereby incorporatedin their entirety by reference, microdroplets having nominal diametersin the range of about 10 nm to about 2 micron can be produced byelectrospray. Various factors as described in such references affect theproduced droplet size. For example, capillary size, liquid feed rate tothe dispensing device, surrounding gas properties, etc. One skilled inthe art will recognize that such factors and others may be modified toproduce microdroplets of desired sizes.

By applying different electrical potential differences between thecapillary tube electrode 18 and the second electrode 21, differentoperating modes can be established. For example, a high positive voltage20 is applied to capillary tube electrode 18 with the grounding of theelectrode 21 to provide the spray 28 with a relatively high positivecharge. For example, the high voltage source 20 may apply a highpositive voltage preferably in the range of about 2000 volts to about50,000 volts and more preferably 2000 volts to about 10,000 volts. Thesecond electrode 21 in such a case may be provided to ground 38 or mayhave a negative voltage connected thereto. With relatively largepotential differences being applied, as described in the above papers,pulsating modes or cone jet modes of operation are achieved. In a conejet mode of operation, a cone shaped liquid meniscus is formed at thedispensing tip 23 whereas in the pulsating mode, the shape of the liquidmeniscus alternates between a cone shape and a round shape. On the otherhand, with relatively low electrical potential differences appliedbetween the capillary tube electrode 18 and the second electrode 21,dripping from the dispensing tip occurs.

One skilled in the art will recognize that a high positive voltage maybe applied to electrode 21 with the tube electrode 18 grounded toprovide a highly negative charge on the particles of the spray 28. Theonly requirement necessary for the potential difference supplied betweenthe capillary tube electrode 18 of the distributor head 19 and thesecond electrode 21 is that the electrical potential difference providesfor a nonuniform electric field for establishment of a charged spray 28.The charge on the particles of the spray 28 must be concentrated suchthat the space charge effect of the charged particles allows forciblecontact with the target cells 40, and preferably, allows for penetrationof such target cells 40.

It is noted that the particle velocity is established primarily by thespace charge effect due to the concentrated charge on the particles ofthe spray. Only secondarily is the velocity of the particles provided bythe attractive forces between the charged spray 28 and the secondelectrode 21. It has been determined that for particles of relativelylarger size, e.g., particles having nominal diameters less than about0.5 microns, less than about 5 percent of the velocity is due to theelectric field created by the applied voltage. Further, for particles ofrelatively smaller sizes, e.g. particles having nominal diameters ofless than about 0.05 microns, less than 1 percent of the velocity is dueto the electric field created by the applied voltage. Initially uponbeing dispensed from the dispensing tip 23, the charged particlevelocity is due to the electric field created by the applied voltage.However, such initial velocity is almost immediately overtaken by thetremendous velocity attainable due to the space charge effect of thecharged particles. The second electrode 21 is primarily used forestablishment of the charged spray forward of the dispensing tip 23, andfurther is used for directing the particles of the spray and containmentthereof.

Although various configurations for the dispensing device may besuitable, the dispensing device 12 preferably includes a capillary tubemade of a suitable material, such as, for example, platinum, silica,etc. for providing the spray 28. For example, the capillary tube mayhave an outer diameter in the preferred range of about 6 μm to about 2.5mm and an inner diameter in the preferred range of about 6 μm to about 2mm. Further, the dispensing device 12 may include a conductive ornonconductive casing concentric to the capillary tube, which is used toprovide a sheath of gas, e.g., CO₂, SF₆, etc., around the capillary tubeto increase the electrostatic breakdown voltage for the capillary tube,e.g., to prevent corona discharge. The use of such a sheath of gas isparticularly beneficial when the spray is created using a high surfacetension liquid, e.g., deionized water. Several detailed configurationsfor the dispensing device 12 are described in further detail below.

The desired velocity to which the particles of the spray 28 areaccelerated depends upon various factors. For example, such factorsinclude but are clearly not limited to the charge on the particles,whether a vacuum chamber is used, the size and density of the particlesas well as the type of target cells 40 to be impacted. Preferably, thedesired velocity is the minimum velocity necessary such that theparticles can penetrate the cell membrane of the target cells 40. Thevelocity necessary to penetrate such cells will be dependent upon thetype of target cell which, for example, may include bacteria, singlecell protozoa, plant pollen, plant protoplast, embryos, callus tissue,animal cells including animal progenitor cells (including, but notlimited to pluripotent cells, stem cells, eggs, oocytes, embryoticcells), animal bone marrow cells and precursor cells, muscle orepidermal cells, epithelial cells, blood cells, isolated tissueexplants, various other plant cells, or various other animal cells. Thetarget cells may be part of a tissue, may be a monolayer of cells, amultilayer of cells, a suspension of cells, as well as being affixed toa surface or may take any other form as would be readily apparent to oneskilled in the art.

With the preferred configurations as described herein, velocities in therange of about 30 m/sec to about 600 m/sec for particles having nominaldiameters in the range of about 2 nm to about 1 μm are possible. Thevelocities on the higher end of the range are primarily due to smallparticle size, high particle charge, and/or reduced pressure. Further,particles can be generated utilizing such a configuration and deliveredto the target surface at rates in the range of about 10⁸ particles persecond to about 10¹¹ particles per second continuously. The particlegeneration rate may be increased by using multiple capillary tubeelectrodes. The preferred velocity, nominally in the range of about 150m/sec to about 300 m/sec, is sufficient to penetrate but not causedamage to most types of target cells.

The spray of particles 28 established by electrospray dispensing device12 when source 22 is a suspension including carrier particles andbiological material is generally formed as previously described hereinby dispensing microdroplets having the carrier particles and biologicalmaterial suspended thereby. Thereafter, the microdroplets evaporateconcentrating the charge of the microdroplets on carrier particles andbiological material which typically becomes associated therewith.Likewise, the spray of particles 28 established by electrospraydispensing device 12 when source 22 is a suspension including bulkbiological material is generally formed as previously described hereinby dispensing microdroplets having biological material suspendedthereby. Thereafter, evaporation of the microdroplets concentrates thecharge of the microdroplets on the biological material. By controllingvarious parameters of the electrospray apparatus, the amount ofbiological material delivered for impact with the target cells 40 can becontrolled. Further, the velocity of such particles may also beenhanced.

Several characteristics that can be controlled include microdropletsize, the concentration of biological materials, and carrier particlesize of the particles suspended in the spray 28. First, velocity of theparticles may be enhanced by controlling particle size, i.e., carrierparticle size. Smaller dimensional particles may enable such particlesto have higher velocities due to space charge effect.

Further, by controlling the size of the sprayed microdroplets and thecarrier particle size, the amount of biological material delivered canbe controlled and higher velocities for the particles can be attained.First, the microdroplet nominal diameter can be controlled. For example,the microdroplet diameter may be controlled by controlling the capillarysize, the liquid feed rate for suspensions, the electrical conductivityof the suspension, etc. The nominal diameter typically falls in theranges as described previously herein.

With the use of carrier particles having smaller nominal diametersrelative to the microdroplets, such as particles having a nominaldiameter in the range of about 2 nm to about 1000 nm, or preferably inthe range of about 10 nm to about 100 nm (or by increasing the size ofthe microdroplets relative to the particles), the amount of charge thecarrier particles can carry is increased. In other words, by increasingthe size differential between the microdroplets and the particles, uponevaporation the carrier particles (e.g., gold) can carry a charge muchhigher than the Raleigh limit for typical liquid suspensions. In thismanner, the space charge effect provides for attainment of a highervelocity such that the particles can penetrate to different depths ofthe cell tissues. Further, by use of a vacuum chamber into which theparticles are sprayed, increased velocities can be achieved.

Further, microdroplets having sizes slightly larger than carrierparticles and/or biological material suspended thereby may be produced.This results in uniform size particles without agglomerates beingformed. The effect of space charge repulsion of the unipolarly chargedparticles keep them separate and prevent particle agglomeration in thespray, as well as provide the particles with the velocity necessary forforcible contact with the target cells, preferably, for penetration ofthe target cells.

Further, by controlling the size of the microdroplet and the size of thecarrier particles, one particle per microdroplet is attainable. With acontrolled flow and known concentration of biological material utilizedin association with the carrier particles, the amount of biologicalmaterial in spray 28, or delivered to the spray area, can be controlledand is reproducible, i.e., can be consistently repeated.

After the microdroplets of liquid suspending the particles and/orbiological material, is dispensed, the solvent of the microdropletsbegins to evaporate decreasing the size of the microdroplet. At thetarget cells 40, typically only the carrier particle having associatedbiological material (or biological material alone in the case of abiological material suspension without carrier particles) remains forimpact with the target cells 40. The spray particle size can be madevery small, as small as a few nanometers in diameter and still attainthe necessary velocity under the effects of space charge. This makes itpossible to deliver biological materials into smaller cells and tissues.

In addition to penetration of the cells as a result of the bombardmentof the cells with material using the present invention, theelectrospraying technique described herein may be used to produceliposome droplets encapsulating biological material, e.g., DNA. Theliposome droplets can be directed by the electric field and distributeduniformly over target cells in manners similar to those describedherein, e.g., movement of the target surface, movement of thedistributor head, etc. As opposed to the penetration of the cells atimpact, the liposomes encapsulating the biological material facilitatetransfer of the material into the cells through fusion of the liposomewith the cell membrane as is known to those skilled in the art. Theliposome droplets may be of varying sizes, e.g., a nominal diameter ofabout 10 nm to about 10 μm. The electrospraying technique used to directthe liposomes onto the cells can be adjusted (e.g., distance of nozzleto target surface can be adjusted, electrical potential or strength ofthe field can be adjusted, etc.) to vary the velocity of the liposomedroplets such that the liposome droplets land appropriately for thefusion mechanism to be accomplished.

One embodiment of an electrospraying apparatus 42 in accordance with thepresent invention is shown in FIG. 2. Generally, the electrospraydispensing device 12 positioned for providing a spray 28 into a chamber16 is substantially equivalent to that described generally with respectto FIG. 1C as indicated by like reference numbers being used for likeelements. However, in the embodiment of FIG. 2, a target surface 14having one or more target cells 40 placed thereon is positioneddownstream from or forward of the dispensing device 12.

The spray 28 has a first electrical charge concentrated on the particlesas previously described herein upon evaporation of the microdroplets inthe electric field created by the high voltage source 20 applied to thecapillary tube electrode 18 and the grounding of target surface 14. Thecapillary tube electrode 18 functions as the first electrode asdescribed with reference to FIG. 1B and the conductive target surface 14functions as the second electrode described with reference to FIG. 1B.With an electrical potential difference established between thecapillary tube electrode 18 and target surface 14, a nonuniform electricfield is provided from the dispensing tip 23 to the target surface 14 toestablish the spray of particles 28 forward of the dispensing tip 23. Inaddition to creating the nonuniform electric field for establishing thespray of particles 28, the conductive target surface 14 connected toground 38 also provides for containment of the particles to a certainarea to allow for forcible contact with the target cells 40.

As shown in FIG. 2, depending on the dispensing device used and othercomponents of the apparatus, the particle suspension provided fromsource 22 may be from a pressurized source. Alternatively, a pressurizedgas source 26 may be utilized in conjunction with feeder 24 or anotherportion of the dispensing device 12 so as to provide pressure todispense the spray 28 into chamber 16. For example, the source 22 may bepressurized in the range of a few tenths of an atmosphere to a few 100atmospheres, or the pressurized gas source 26 utilized may be a gas suchas, for example, carbon dioxide, ambient air, hydrogen, helium,nitrogen, and be at similar pressures.

The target surface 14 may be any suitable surface for placement oftarget cells. For example, the target surface may be an electricallyconducting surface connected to an electrical ground or charge.Generally, the cells may be made conductive to the target surface by thenatural moistness of the cells or made conductive by any other manner,e.g., coating, nutriant solutions. The target surface 14 is asubstantially horizontal surface capable of supporting the target cellsthereon. The electrical potential or ground may be applied to the targetsurface such that a portion or the entire surface attracts the spray,e.g., the particles are directed to particular areas of the targetsurface by the electrical field set up by the potential differenceapplied between the distributor head and the target surface. Being ableto direct the spray to a particular portion of the target surface isbeneficial in that overspray is avoided. In other words, the spray isattracted to a portion of the target surface having a voltage appliedthereto, e.g., a portion insulated from the other portions, where targetcells have been positioned. It is even possible to adjust the electricalfield between the distributor head 19 and the target surface 14 suchthat the particles are directed from one position of the target surfaceto another, such as by switching mechanisms or alternative voltagesources applied thereto.

Preferably, the target surface 14 is moveable along the x, y, z axes asindicated generally with arrows 33 and 34. The target surface 14 isprovided with, and supported by, a movable positioning member (notshown) which enables it to move the target surface along such axes. Forexample, the target surface may be moved either closer to or fartheraway from the electrospray dispensing device 12. The distance betweenthe dispensing tip 23 of the distributor head 19 in the chamber 16 andthe target surface 14 is preferably in the range of about 5 mm to about3 cm depending on the desired electric field and spray area (D) desired.However, this distance may vary depending on the specific application,and it is apparent that the spray area D will have a lesser diameter asthe dispensing tip 23 of the distributor head 19 and target surface 14are moved closer to one another.

Since all the particles of the spray 28 carry the same polarity chargeas they are dispensed into the chamber 16, the particles tend to repeleach other and avoid agglomeration. The electrospray technique can coverthe spray area D uniformly. It should be noted that the repulsion of thesame polarity charged particles will, at least in part, determine thespread of the spray 28 dispensed in the chamber 16.

FIG. 3 diagrammatically shows the electrospraying apparatus 42 of FIG. 2with the addition of an external electrostatic field 50 for furtheraccelerating the charged particles of spray 28 dispensed into chamber16. The external electrostatic field 50 is provided using ringelectrodes 52 having a negative high voltage supply 54 connected theretoand further connected to ground 56. The field accelerates the chargedparticles dispensed into the chamber 16 through the ring electrodes. Insuch a manner, the particles are further accelerated towards groundedtarget surface 14. The voltages applied to the ring electrodes may be inthe preferable range of about 200 V to about 5 kV.

It should be readily apparent to one skilled in the art that theacceleration of the charged particles of the spray 28 by the externalelectric field 50 may be needed for accelerating the particles to adesired velocity necessary for penetrating certain target cells 40 ontarget surface 14. However, in accordance with the present invention,such added acceleration is generally unnecessary as the space chargeeffect provides the necessary velocity for such penetration.

FIG. 4 diagrammatically illustrates the electrospraying apparatus 42 asshown in FIG. 2 but further includes a placement control member 70.Placement control member 70 includes an opening 71 which allows aportion of the particles of spray 28 therethrough for impact with targetcells 40. In such a manner, the particular target cells 40 to beimpacted can be controlled.

FIG. 5 is a diagrammatical illustration of an alternativeelectrospraying apparatus 100 which is similar to the electrosprayingapparatus 42 of FIG. 2 but which includes several additional beneficialcomponents. The electrospraying apparatus 100 includes electrospraydispensing device 112 substantially identical to that shown in FIG. 1but which dispenses the spray 128 into a vacuum chamber 116 evacuated byvacuum pump 142. The velocity of the particles of spray 128 due to thespace charge effect is generally greater as the pressure in chamber 116is decreased. Preferably, the pressure in the chamber is in the range ofabout 1 atmosphere to about 0.1 atmosphere.

The electrospray apparatus 100 further includes a target surface 114whereon target cells 140 are placed and which is connected to ground138. The target surface is rotatable around axis 119 utilizing amotorized positioning member 115. The target surface 114 can then berotated and a more uniform distribution of the particles of spray 128 isdelivered to the target cells 140. Further, the dispensing device 112 ismovable along the x, y, z axis as represented generally by arrows 131and 132. As such, particles can be delivered for impact with the entirearea of the rotating surface 114. For example, the dispensing device 112can be positioned away from the axis 119 (e.g., half the distancebetween axis 119 and the edge of the rotatable target surface 114). Inthis manner, the spray 128 can be uniformly distributed on the cells onthe target surface 114 as the target surface rotates.

FIG. 6 diagrammatically illustrates an alternative electrosprayingapparatus configuration 200. The electrospraying apparatus 200 includesa conveyer system 260 which is positioned relative to dispensing device212. Dispensing device 212 is like an electrospray dispensing devicedescribed herein. The electrical potential difference for providing thespray from the dispensing device 212 is applied using voltage source 220and grounding the conveyor system 260. The conveyer system 260 includestarget surface 262 which is moved by motorized element 264. In such amanner, the continuous providing of spray 228 with the continuousmovement of target surface 262 having target cells 240 placed thereonprovides for a mass production system for transfer of biologicalmaterial to target cells.

It will be readily apparent that the cells to be modified by thebiological material may be in their natural state, e.g., in situ. Suchcells may be treated while in the body of an animal, i.e., in vivo, orwhen such cells are removed from the body, i.e., ex vivo. For example,tissues which can be bombarded include human tissue or other animaltissues such as epidermal tissue, organ tissue, tumor tissue, planttissue and like, while in the body or removed from the body. A portableelectrospraying apparatus for gene therapy or other specialized in situapplications, e.g., immunization, may be used. For example, in such aportable configuration, the target cells to be impacted by the chargedparticles may be situ cells, as opposed to the cells being on a targetsurface. An illustrative portable electrospraying apparatus is generallydescribed below with reference to FIG. 9 and will generally includeelements or components similar in function to the configuration of FIG.1C.

It should be apparent to one skilled in the art that the variouselements described in reference to FIGS. 1-6 may be combined in avariety of manners and each alternative configuration of theelectrospraying apparatus described herein is for illustration purposesonly. For example, the vacuum chamber 116 described with reference toFIG. 5 may be utilized with the electrospray apparatus of FIG. 4, theplacement member 70 described with reference to FIG. 4 may be utilizedin the electrospray apparatus 42 of FIG. 2, the conveyer system 260 asdescribed with reference to FIG. 6 may be utilized with the externalelectric field 50 as described with reference to FIG. 3, etc.

FIG. 7 is a more detailed diagram of one configuration of a portion 300of the electrospraying apparatus shown generally in FIG. 2 including adispensing device 314 according to the present invention. As shown inFIG. 7, spray 328 is sprayed into a chamber 303 defined by a housing 302having an axis 301 therethrough. The housing 302 includes a first end304 and a second end 306 connected therebetween with a cylindrical wallabout axis 301. Preferably, the housing 302 is a vacuum chamber whichcan be evacuated as described further below. It will be recognized thatvarious configurations may be selected for creating the housing 302 andthat the present invention is not limited to any particularconfigurations. The housing 302 is generally formed of insulativematerials. For example, the cylindrical wall enclosure 308 is preferablya plexiglass cylindrical wall for visibility while the first and secondends 304, 306 may be formed of various insulative materials. First end304 may also be formed of conductive portions to facilitate applicationof voltages or ground to the capillary tube 320.

The second end 306 of the housing 302 includes an end element 311connected to the cylindrical walls 308. Positioned relative to an uppersurface 370 of the end element 311 is a target platform 312 upon whichtarget cells can be positioned. For example, a tube, dish, or any otherstructure may be positioned on the platform 312 which includes cells orthe cells may be positioned on the platform 312 without any additionalstructure. Further, a rotatable micrometer adjustment mechanism 310 isprovided through a lower surface 371 of the end element 311 for contactwith platform 312 such that the height of the platform 312 can bevaried, e.g., the distance between the target cells 340 and thedispensing tip 380 of the dispensing device 314 can be adjusted. Theplatform 312 is formed of a conductive material, e.g., stainless steel,and may function as the second electrode of the dispensing device 314for establishing spray 328 from the dispensing tip 380 of the dispensingdevice 314.

The first end 304 of the housing 302 includes a distributor head 316extending therethrough having an axis that is coincident with axis 301for use in establishing the spray 328 in the chamber 303 in combinationwith conductive platform 312. The distributor head 316 includes acapillary tube 320 having an axis therethrough coincident with axis 301.The capillary tube 320 includes a first end 330 sealingly positioned inaperture 385 of the first end 330 by conductive sealing element 337 atthe upper surface 383 of the first end 304. The capillary tube 320further includes a second end 332 positioned for dispensing spray 328 asdesired. The capillary tube 320 may be made of any suitable material,such as, for example, platinum, silica, stainless steel, etc. and may beof any suitable size. For example, the capillary tube may preferablyhave an outer diameter in the range of about 8 μm to about 2.5 mm, andan inner diameter in the preferred range of about 6 μm to about 2 mm.More preferably, the inner diameter of the capillary tube is in therange of about 10 μm to about 200 μm.

Further, the distributor head 316 includes a nozzle portion or casing322 which as illustrated in FIG. 7 is an elongate substantiallycylindrical metal casing concentric with the capillary tube 320.However, the casing 322 can be conductive or nonconductive. Further, thecasing 322 can take any configuration or shape which allows for the flowof a sheath gas about the capillary tube 320. Together, in thisparticular embodiment, the capillary tube 320 and the casing 322 formthe capillary tube electrode of the distributor head 316 for use inproviding the spray 328 into the chamber in conjunction with theconductive platform 312. The casing or nozzle portion 322 includes afirst end portion 336 which tapers at section 335 thereof to a narrowersecond end portion 338. The second end portion 338 extends from thetapered section 335 and is concentric with the second end 332 of thecapillary tube 320. The narrow end of the tapered section 335 extends apreferable distance of about 5 mm to about 5 cm from the lower surface385 of the first end 304. The outer diameter of the second end portion338 is preferably in the range of about 2 mm to about 5 mm and the innerdiameter of the second end portion 338 is preferably in the range ofabout 0.1 cm to about 0.2 cm. The second end 332 of the capillary tube320 extends beyond the second end portion of the metal casing or nozzleportion 322 towards the target cells 340 by a distance of preferablyabout 2 mm to about 5 mm. The nozzle portion 322 is formed of anysuitable metal or nonconductive material such as stainless steel, brass,alumina, or any other suitable conductive or nonconductive material. Thenozzle portion 322 is spaced from the capillary tube 320 by spacers 326or other spacing structures. For example, a metal casing 322 may bedeformed at particular portions, such as pin points or depressions, tocreate a neck for centering the capillary tube 320 therein.

The capillary tube electrode may take one of many configurations.However, of primary importance is that the capillary tube electrodeprovide an electrode for creating the nonuniform electric field andprovide at least a gas sheath about the capillary tube to avoid coronadischarge if spraying high surface tension liquids, e.g., deionizedwater. For example, in an electrospraying apparatus wherein the spray isestablished in a chamber, the capillary tube electrode may just includea capillary tube itself, as opposed to requiring a casing such as metalcasing 322 to provide an annular space for flow of the sheath gas. Insuch a configuration, the chamber may be flooded with the gas forpreventing corona discharge. Further, when spraying liquids other thanhigh surface tension liquids, the gas sheath may not be required.

A gas inlet 348 is provided in the first end 304 of housing 302 to allowfor input of a stream of electro-negative gases, e.g., CO₂, SF₆, etc.,to form a gas sheath about the capillary tube 320. The inlet isconfigured for directing a stream of an electro-negative gas in anaperture 350 between the concentric capillary tube 320 and the nozzleportion 322. This gas sheath allows the applied voltage to be raised tohigher levels without corona discharge, e.g., the electrostaticbreakdown voltage for the capillary tube electrode is increased. Theentire portion of end 304 or portions thereof may be formed ofconductive materials to facilitate application of a voltage or ground tothe capillary tube electrode. For example, sealing elements 337 may benonconductive, but is preferably conductive to facilitate application ofa voltage or ground to capillary tube 320.

The first end 304 further includes an exit port 354 for gases to exitthe chamber 303. For example, the exit port 354 may open into an annularchamber 389 defined in the first end 304 having a bottom face plate 390having a series of holes for allowing flow from the chamber 303 outthrough the exit port 354. A vacuum pump may be connected to the exitport 354 for evacuating the chamber 303 to a low pressure. For example,preferably, the pressure in the chamber is in the range of about 1atmosphere to about 0.1 atmosphere. Further, instead of or in additionto providing the gas sheath between the capillary tube 320 and thenozzle portion 322, the chamber 303 may be flooded with a gas throughthe exit port 354 to increase the electrostatic breakdown voltage forthe capillary tube electrode.

In one embodiment, the chamber 303 is flooded with the gas through theexit port 354 and then a flow in the preferred range of about 5 cc/minto about 200 cc/min is continued through the exit port 354. Any port tothe chamber 303 may be used for exit of gas from the flooded chamber,e.g., such as a port that is available for sensing pressure (not shown)in the chamber. When the chamber 303 is flooded, the gas sheath betweenthe capillary tube 320 and the nozzle portion 322 may not be necessary.As such, flooding of the chamber is an alternative to the use of such agas sheath between the capillary tube 320 and the nozzle portion 322.

To establish the spray 328 in the chamber 303, biological material isprovided, e.g., suspended in a solution, and received in the first end330 of the capillary tube 320. Preferably, the flow rate of thesuspension may be in the range of about 0.01 μl/min to about 5 μl/min.Preferably, a relatively high voltage, for example, in the range ofabout 2000 volts to about 6000 volts, may be applied to the platform 312relative to the capillary tube 320 which is electrically grounded (orvice versa) to establish the potential difference between the first andsecond electrode of the spraying apparatus. In this particularillustrative configuration, capillary tube 320, metal casing 322, andsealing element 337 are conductive. Spray 328 is established forward ofthe dispensing tip 380 of the second end 332 of the capillary tube 320per a mode of operation as previously described. The potentialdifference between the electrodes establishes an electric fieldtherebetween causing the formation of a smaller filament at the meniscusformed at the dispensing tip 380 while attracting the suspensiondownward toward the target cells.

FIG. 8 is a more detailed diagram of an alternate capillary electrodeconfiguration 400 for the distributor head 316 of FIG. 7. Like referencenumbers are used in FIG. 8 for corresponding like elements of FIG. 7 tosimplify description of the alternate capillary configuration 400.Generally, the alternate capillary electrode configuration 400 issubstituted for or replaces the single capillary tube 320 of thestructure shown in FIG. 7.

The capillary electrode configuration 400 includes a first capillarytube 412 having an axis coincident with axis 301 for receivingbiological material from a source, e.g., a suspension of biologicalmaterial. Further, a second capillary tube 414 is concentric with thefirst capillary tube 412. An annular space 487 between the inner andouter capillaries 412, 414 is used to direct a stream of electrolyteliquids of controlled conductivities to the dispensing tip 495 for usein establishing the spray forward thereof. The use of an electrolytesolution flowing to the dispensing tip 495 for establishing the spray ofmicrodroplets therefrom, allows the suspension of biological material tobe prepared with deionized water which has characteristics, e.g., pH,that do not disturb the biological material properties. With use of theelectrolyte solution, sufficient charge is achieved on the microdropletswhich thereafter concentrates on the particles of the spray to allowspace charge effects of the particles to attain sufficient velocitiesfor penetrating target cells. Without the second flow of electrolytesolution, an electrolyte solution may need to be added to the suspensionto achieve such charge concentration. Further, the electrolyte solutioncharacteristics, e.g., conductivity, can be changed to adjust the chargeconcentrated on the particles without the need to change the suspensioncharacteristics. The stream of electrolyte liquids is directed in theannular space 487 such that it comes into contact with the suspensionproximate the dispensing tip 495.

In more detail, the housing portion 430 includes an aperture 483extending from a first end 480 of the housing portion 430 to a secondend 482 thereof. An inlet port 420 opens into the aperture 483. Theinlet port 420 receives a flow of electrolyte liquids 422 to be directedin the annular space 487 about the capillary tube 412. The firstcapillary tube 412 has a first end 413 and a second end 415. Thecapillary tube 412 is positioned in the aperture 483 of the housingportion 430 of generally T-shaped configuration. The first end 413 ofthe capillary tube 412 is sealed to housing 430 using conductive element431 at the first end 480 of the housing portion 430. The capillary tube412 extends from the second end 482 of the housing portion 430 and withthe second capillary tube 414 forms the annular space 487.

The second capillary tube 414 includes a first end 490 and a second end491. The second capillary tube 414 is positioned so that it isconcentric with the first capillary tube 412. The first end 490 of thesecond capillary tube 412 is coupled to the second end 482 of thehousing portion 430 using conductive element 432. Further, the secondend 491 of the second capillary tube 414 is held in place relative tothe nozzle portion 322 by spacers 326. The second capillary tube 414extends beyond the first capillary tube 412 a predetermined distance inthe direction of the target cells of preferably about 0.2 mm to about 1mm. The portion of the second capillary tube 414 at the dispensing tip495 which extends beyond the first capillary tube is tapered at a 60degree to 75 degree angle for obtaining stable spray pattern andoperation mode, i.e., consistent spraying patterns. Without the taper,intermittent operation may occur. Further, the second capillary tube 414extends beyond the second end 338 of the nozzle portion 322 apredetermined distance (d5), preferably about 2 mm to about 5 mm. Thefirst capillary tube 412 has preferable diameters like that of capillarytube 320 of FIG. 7. The second capillary tube concentric with the firstcapillary tube has a preferable outer diameter of about 533.4 μm toabout 546.1 μm and a preferable inner diameter of about 393.7 μm toabout 431.8 μm. The gap d6 at the tip of the second capillary tube 414is preferably in the range of about 10 μm to about 80 μm. The otherpreferred configuration parameters are substantially equivalent to thatdescribed with reference to FIG. 7.

In such a configuration, dual streams of liquids are provided forestablishing a spray from dispensing tip 495 of the apparatus when asuspension of biological material or a suspension of carrier particlesand biological material are used. This provides the benefits aspreviously described. Further, a gas sheath may also be provided throughinlet port 348 as previously described with reference to FIG. 7. Yetfurther, the first capillary tube 412 may extend beyond the end of thesecond capillary tube 414, e.g., the dispensing tip is formed at the endof first capillary tube 412 which is closer to the target cells than theend of the second capillary tube 414. In other words, the suspension maycontact the electrolyte solution before exiting the dispensing tip 495or the suspension may contact the electrolyte solution upon exiting theend of the first capillary tube 412. Further, the second capillary tubemay take various other configurations to form the space for providingthe electrolyte solution to the dispensing tip, e.g., not necessarily acapillary tube structure.

The first or center capillary may be used to spray suspensions ofbiological material with or without the use of carrier particles. Therate of flow of such suspensions may vary. Preferably, the flow rate isabout 0.01 μl/min to about 2.0 μl/min. The annular space between theinner 412 and outer 414 capillaries is used to direct the stream ofelectrolyte liquids of controlled conductivities. The rate of flow ofsuch electrolyte liquids may vary. Preferably, the flow rate is about0.1 to about 5 μl/min. For example, such electrolyte solutions mayinclude deionized water with a trace of nitric acid, nutrient liquidsused for growing cultured cells, or any other suitable component forbiological material suspensions or target cells. The electricalconductivity of such electrolyte liquids is preferably in the range ofabout 60 μΩ⁻¹/cm to about 80,000 μΩ⁻¹/cm.

In addition to controlling conductivity and therefore the charge of theparticles sprayed, the dual stream of liquids can further be used forother purposes. For example, the outer stream may be a suspension ofliposomes that are sprayed with a suspension of other biological, e.g.,DNA, provided through the center capillary. As such, the outer flow ofthe suspension includes an agent, e.g., liposomes, which is used topromote penetration of the target cells, e.g., dissolve the outerlinings.

FIG. 9 shows an illustrative diagram of a dispensing device 500 for acompact pen-like electrospraying apparatus in accordance with thepresent invention that may be used for introduction of biologicalmaterial into cells, such as in situ cells, e.g., human tissue or otheranimal tissues such as epidermal tissue, organ tissue, tumor tissue,plant tissue and the like. The dispensing device 500 includes acapillary tube 502 and a nozzle portion 504 configured substantially thesame as described with reference to FIG. 7. The apparatus furtherincludes a gas sheath 509 provided between the capillary tube 502 andthe nozzle portion 504. The main difference between the apparatus asshown in FIG. 7 and that of FIG. 9 is that a ring electrode 530 used forestablishing the spray at the dispensing tip 531 is positioned at thesecond end 533 of a cylindrical insulative jacket 514 concentric withand preferably in contact with the nozzle portion 504 along at least aportion of a first end 535 of the jacket 514. With use of such aconfiguration, a chamber is eliminated.

EXAMPLE 1

Using an apparatus equivalent to that shown in and described withreference to FIG. 7 modified with the dual capillary tube distributorhead 400 shown in and described with reference to FIG. 8, biologicalmaterial transfer was successfully accomplished. The apparatus used wasconfigured with a center capillary tube 413 having an outer diameter ofabout 229 μm to about 241 μm and an inner diameter of about 89 μm toabout 127 μm. The second capillary tube 414 concentric with the centercapillary tube had an outer diameter of about 533 μm to about 546 μm andan inner diameter of about 394 μm to about 432 μm. The distance d1 shownin FIG. 8 from the end of tapered section 335 to the end of the metalcasing 322 is about 2 cm. The diameter d2 of the first end 336 of thenozzle portion or metal casing 322 is about 0.5 cm. The outer diameterd4 of the second end 338 of the nozzle portion 322 is about 1715 μm toabout 1740 μm and an inner diameter d3 of about 1333 μm to about 1410μm. The distance d5 from the tip of the second end 338 of the nozzleportion 322 to the tip of the end of the second capillary tube 414 isabout 5 mm. The gap d6 at the tip of the second capillary tube 414 isabout 40 μm.

The dispensing device was constructed of various materials. Primarily,the conductive elements were constructed of stainless steel, the chamberwall was made of plexiglass, and the insulative parts such as portionsof the ends 304 and 306 were made of a plastic, black delrin, material.

The biological material source was a suspension of plasmid and Auparticles having 5 and 10 nanometer diameters (available from Sigma ofSt. Louis, Mo.). The plasmid was a commercially available plasmidincluding EGFP gene (Enhanced Greeen Fluorescent Protein from a JellyFish). The plasmid is available under the designation EGFP from Clontechof Palo Alto, Calif. The plasmid was resuspended for use at 0.05μgrams/μliter in deionized water with a concentration of 0.01 percent Auparticles.

The target cells were African Green Monkey fibroblast cells (COS-1)available from the American Type Culture Collection (Rockville, Md.)under the designation ATCC CRL-1650, Simian fibroblast like cells fromkidney transformed with SV40 virus. The target cells were a monolayer atan estimated concentration of about 800 cells/cm². The target cells arein a Dulbecco's Modified Eagle Medium (DMEM-Hi) which includes 10percent Fetal Calf Serum and 90 percent deionized water (available fromGibco/BRL of Rockville, Md.).

The electrospray was operated in a pulsating mode in a flooded chamber302. The chamber 302 was flooded using a 50 cc/min flow of CO₂ throughport 354. No gas sheath was provided about the second capillary tube414. A voltage of 4300 volts was applied to conductive element 312 asshown in FIG. 7. The distance from the dispensing tip 495 of the secondcapillary tube 414 to the target cells 340 was about 2.5 cm. The cellswere provided in a small well 396 (cut from a 12-well culture dishavailable from Corning of Cambridge, Mass.) formed of optically clearvirgin polystyrene treated with optimal cell attachment and having adiameter of about 22 mm. The well 396 was placed on the platform 312 ofthe second end 306 of the housing 302. Conductive wires 397 wereprovided from inside the well 396 to the conductive platform 312 tobleed off stray charge and to form the spray as well.

The sheath liquid provided in the annular space 487 between the firstand second capillary tubes 412, 414 was a 1 μl/min flow of deionizedwater plus a trace amount of nitric acid of a ratio of about (1:50) withan electrical conductivity of about 300 μΩ⁻¹/cm. The suspensiondescribed above was provided by a syringe pump available under thedesignation of Harvard “33” Double syringe pump from Harvard Apparatusof Holliston, Mass. at a rate of 1.0 μl/min.

The cells were sprayed for about 2 minutes at a temperature of 20° C.and a pressure of 1 atmosphere. The well containing the target cells wasplaced in an incubator (available from NAPCO of Landrum, S.C.) for 1.5days at a temperature of about 37° C., i.e., the time for cells todivide themselves and express fluorescence. A UV microscope availableunder the designation of Nikon Inverted Fluorescent Microscope fromFryer Co. of Minneapolis, Minn. was used to visually note thefluorescence. Approximately 40 percent to 60 percent of the cellsfluoresced. As fluorescence was noted, introduction of biologicalmaterial into the cell was successful.

EXAMPLE 2

The same setup of Example 1 was used. The only difference was that Auparticles were not added to the suspension and the voltage applied tothe element 312 was 5600 volts such that the dispensing device wasoperated in cone jet mode. Again, the UV microscope was used to visuallynote the fluorescence. Approximately 40 percent to 60 percent of thecells fluoresced. As fluorescence was noted, introduction of biologicalmaterial into the cell was successful.

All patents and references disclosed herein are incorporated byreference in their entirety, as if individually incorporated. Further,although the present invention has been described with particularreference to various embodiments thereof, variations and modificationsof the present invention can be made within the contemplated scope ofthe following claims as is readily known to one skilled in the art.

1. An apparatus for coating particles, the apparatus comprising: asource comprising at least one suspension, wherein the source comprisingthe at least one suspension comprises at least particles and coatingmaterial; a capillary tube electrode, wherein the capillary tubeelectrode includes a capillary tube having a first open end and a secondopen end, the capillary tube operatively connected to the source toreceive a flow of at least the suspension at the first open end thereof;and an electrode isolated from but positioned in proximity to the secondopen end of the capillary tube, wherein a nonuniform electrical field iscreated between the capillary tube electrode and the electrode isolatedtherefrom such that a spray of microdroplets suspending at least theparticles is provided from the second end of the capillary tube, andfurther wherein the particles are coated with at least a portion of thecoating material as the microdroplet evaporates.
 2. The apparatus ofclaim 1, wherein the particles comprise carrier particles and thecoating material comprises biological material.
 3. The apparatus ofclaim 1, wherein the particles comprise biological material particles.4. The apparatus of claim 3, wherein the coating material comprises afacilitating transfer material.
 5. The apparatus of claim 1, wherein anelectrical charge is concentrated on the coated particles as themicrodroplet evaporates, and further wherein a space charge effect ofthe concentrated electrical charge substantially prevents agglomerationof the coated particles.
 6. The apparatus of claim 5, wherein theelectrical charge concentrated on a coated particle is in the range ofabout 80 percent to about 95 percent of a maximum charge that is held bythe microdroplet.
 7. The apparatus of claim 1, wherein the particleshave a nominal diameter of about 2 nanometers to about 1 micron.
 8. Theapparatus of claim 7, wherein the particles have a nominal diameter ofabout 10 nanometers to about 100 nanometers.
 9. The apparatus of claim1, wherein the particle source provides a continuous source of thesuspension to the capillary tube.
 10. The apparatus of claim 1, whereinthe capillary tube electrode further comprises a casing concentric withat least a portion of the capillary tithe between the first and secondopen ends thereof, the second open end of the capillary tube extendingbeyond the casing a predetermined distance, and further wherein theapparatus includes a gas source providing a gas to be received betweenthe capillary tube and the concentric casing.
 11. An apparatus forcoating particles, the apparatus comprising: a particle sourcecomprising at least particles to be coated; a coating material sourcecomprising at least coating material; a capillary tube electrode havinga dispensing tip, wherein the capillary tube electrode includes: a firstcapillary tube having a first open end and a second open end, the firstcapillary tube operatively connected to receive a flow of at least oneof particles and coating material at the first open end thereof, and asecond capillary tube concentric with at least a portion of the firstcapillary tube, wherein at least one of the particles and the coatingmaterial is received in an annular opening defined between the first andsecond concentric capillary tubes; and an electrode isolated from butpositioned in proximity to the dispensing tip of the capillary tubeelectrode, wherein a nonuniform electrical field is created between thecapillary tube electrode and the electrode such that a spray ofmicrodroplets suspending at least particles is provided from thedispensing tip, and further wherein upon evaporation of themicrodroplets the particles are coated with the coating material. 12.The apparatus of claim 11, wherein the capillary tube electrode furtherincludes a casing concentric with at least a portion of the secondcapillary tube between a first and second open end thereof, the secondopen end of the second capillary tube extending beyond the casing apredetermined distance, and further wherein the apparatus includes a gassource providing a gas to be received between the second capillary tubeand the concentric casing.
 13. The apparatus of claim 11, wherein anelectrical charge is concentrated on the coated particles as themicrodroplet evaporates, and further wherein a space charge effect ofthe concentrated electrical charge substantially prevents agglomerationof the coated particles.
 14. The apparatus of claim 13, wherein theelectrical charge concentrated on a coated particle is in the range ofabout 80 percent to about 95 percent of a maximum charge that is held bythe microdroplet.
 15. The apparatus of claim 11, wherein the particleshave a nominal diameter of about 2 nanometers to about 1 micron.
 16. Theapparatus of claim 15, wherein the particles have a nominal diameter ofabout 10 nanometers to about 100 nanometers.
 17. The apparatus of claim11, wherein the particle source comprises at least one suspensioncomprising biological material particles.
 18. The apparatus of claim 11,wherein the particle source comprises biological material particles. 19.The apparatus of claim 11, wherein the coating material comprises afacilitating transfer material.